How Are Hurricanes Classified?



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Hurricanes are tropical cyclones with winds of 74 miles per hour or greater. They usually occur in the western Atlantic Ocean. The Saffir-Simpson Hurricane Damage-Potential scale is a tool for measuring the disaster potential of a hurricane's winds and its accompanying storm surge (the wall of water that rushes onshore as the eye of a hurricane passes overhead). The purpose of the scale is to help disaster agencies gauge the potential danger posed by these storms and to determine whether or not to evacuate coastal residents.

The scale, on which each hurricane is assigned a number 1 through 5, was developed in 1971. The creators of the scale are Herbert Saffir, the engineer who designed Miami's hurricane-proof building code, and Robert Simpson, former director of the National Hurricane Center.

Saffir-Simpson Hurricane Intensity Scale
Central pressure Wind speed Storm surge
Scale number (category) mb in. mi/hr km/hr ft m Damage
1 >980 >28.94 74-95 119-154 4-5 1-2 Minimal
2 965-979 28.50-28.91 96-110 155-178 6-8 2-3 Moderate
3 945-9643 27.91-28.47 111-130 179-210 9-12 3-4 Extensive
4 920-944 27.17-27.88 131-155 211-250 13-18 4-6 Extreme
5 <920 <27.17 >155 >250 >18 >6 Catastrophic

Damage categories:

Minimal—No real damage to building structures. Some tree, shrubbery, and mobile home damage. Coastal road flooding and minor pier damage.

Moderate—Some roof, window, and door damage. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood two to four hours before center of storm arrives. Small craft can break moorings (equipment such as anchors) in unprotected areas.

Extensive—Some structural damage to small or residential buildings. Mobile homes destroyed. Flooding near coast destroys structures and flooding of homes 5 feet (1.5 meters) above sea level (level of the ocean's surface) as far inland as 6 miles (9.5 kilometers).

Extreme—Extensive roof, window, and door damage. Major damage to lower floors of structures near the shore, and some roof failure on small residences. Complete beach erosion. Flooding of terrain 10 feet (3 meters) above sea level as far as 6 miles (9.5 kilometers) inland requiring massive residential evacuation.

Catastrophic—Complete roof failure to many buildings; some complete building failure with small utility buildings blown away. Major damage to lower floors of all structures 19 feet (5.75 meters) above sea level located within 500 yds (547 meters) of the shoreline. Massive evacuation of residential areas on low ground 5 to 10 miles (8 to 16 kilometers) from shoreline may be required.

Sources: Bair, Frank E. The Weather Almanac, 6th ed., p. 42; The Public Health Consequences of Disasters 1989, p. 34; Williams, Jack. The Weather Book, p. 137.

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